Sound producer



Oct. 13 1925 a H. C. HAYES soimn PRODUCER Filed March 2, 1925 gwue/ivtox, HARVEY CHAYES Patented Oct. 13, 1925.

UNITED STATES rssmsi PATENT OFFICE.

HARVEY G. HAYES, OF WASHINGTON, DISTRICT'OF GOLUM'BIA.

SOUND PRODUCER.

Application filed March 2, 1925. Serial No. 12,602.

To all whom it may concern:

Be it known that I, HARVEY C. HAYES, a citizen of the U'nited States of America, and a resident of Washington, District of Columbia, have invented new and useful Improvements in a Sound Producer, of which the following is a specification.

My invention relates generally to an apparatus for converting electrical energy mto sound energ but more particularly to a sound producer in which distortion has bee eliminated.

Another object of my invention is the employment of a designed driving mechanism in a reproducer, the fundamental resonance period of which is well above the highest frequency required for reproduction.

A further object is to make the restoring forces great in proportion to the moving mass. I

With these and other-objects in view, my invention will be best understood by reference to the accompanying drawings in which Figure 1 is a cross sectional view of a preferred embodiment of my invention, Figure 2 is a vertical section along the line 2-2 of Figure 1, and Figure 3 is a cross section of a telephone receiver employing my invention, Figure 4 is a vertical sectlon along the line 44 of Figure 3, Figure 5" shows an embodiment wherein the magnetic field .is directed along the diameter of the magnetic ring, and Figure 6 is the adaptation of my invention to a phonograph.

The transformation of electrical energy into sound energy in general requires some mechanism whereby a reci rocating mechanical motion can be pro uced-through the action of the fluctuating or alternating electrical current. This motion may be imparted to a diaphragm directly as in the ordinary single or double pole telephone or it may be imparted through a member linked with the diaphragm. All such sound reproducers are resonant at one or more frequencies and as a result generate sound having these frequencies with greater eificiency and intensity than they do the other frequencies. Most sounds arenot pure but embody a wide range of frequencies, some of which are equal to the resonant frequencies of the reproducers and these components are reproduced with an intensity out of proportion with the other components.

especially when the sound generated is the reproduction of an original sound as in the case of telephone conversation or the reception of radio broadcasting.

Two lines of endeavor have been followed to avoid such distortion. One consists in. damping the motion of the moving parts sufiiciently to prevent the building up of resonance conditions and the other consists 1n so designing the driving mechanism that its fundamental resonance period is well above the highest frequency that the device will be called upon to reproduce. Under such conditions the motions produced by the action of the electrical current will be true forced vibrations and all frequencies will be reproduced with about equal efficiency. The device to be describedis this latter class.

The efficiency of a sound generaton employing forced vibrations alone is largely dependent on the inertia of the movin member; The restoring forces brought into play when the moving member is displaced from its osition of equilibrium must be great if t e natural period of vibration is to be kept high and such restoring forces consequent magnetic poles, or in other words, magnetic poles located within the body of the metal and not at its free ends.

Referring particularly to Figure 1, nu-

meral 1 represents a ring of rectangular I cross-section and made of magnetic material capable of being permanentlvmagrietized.

The location of the two poles is shown respectively by a plus and minus sign. Memhers (2) and (3) are made of soft magnetic material. These members overlap in such a way as to leave an air gap as shownin Figure 2. Numeral (4) represents a magnetlc armature passing through the air gap and centered therein so as to leave a slight clearance between the armature (4) and the two magnetic pole pieces (2) and (3). Numerals(5) and (6) refer to the current carrying coils which may be con.- nected in series or parallel with the electrical driving circuit but in either case the connections must be so made that the current in the two coils has opposite direction.

Under such conditions the center of the armature (4) becomes a positive or negative pole whenever a current passes through the two coils, the sign of this pole being dependent upon the direction of the current and its strength being dependent upon the strength of the current. The driving force depends upon the reaction of the magnetic field of the air gap upon the consequent pole ofthe armature. The direction of this force varies with the direction of the current. It will therefore be seen that a fluctuating or alternating current will cause the armature (4) to move back and forth between the pole pieces (2) and (3).

The armature (4) 1s placed under'tension by means of nut (7) and the restoring force can be made great or small by varying the tension. This permits the use of a ve light armature, the natural period of whic can be made high when it is desired to generate distortionless sounds and of proper linked to the armature value to tune the same to any particular frequency when it is desired to generate sound of that frequency efiiciently. Stated otherwise, the device described is a highly tuned sound generator, the design and principle of operation of which permits its resonance frequency to be varied at will through a wide range of frequencies, the upper limit of which is sufliciently high to make the device non-resonant over the range of frequencies covered by the voice or by most musical instruments.

The sound generating diaphragm (9) is (4) by means of a light rod (10) that passes through a small slot 8 in one of the pole pieces.

Figures 3 and 4 show the'device'described as embodied in a telephone receiver. Figure 5 shows a desi n wherein the magnetic field is directed ong a diameter of the magnetic ring 1 instead of along its axis. Here the direction of motion of the armature (4) is at right angles to that shown in the other figures. This arrangement is advantageous forid-riving a diaphragm through the medium of a lever and as particularly illustrated in Figure 6 finds immediate application in case of a phonograph where by resting the tip of the'needle on the armature (4), the phonograph is transformed into a loudspeaker.

Having described my invention, what I claim is:

1. An electromagnetic sound reproducing device comprising an electromagnetic operating mechanism including a pair of solenoids, an (armature in' the form of a magnetic rod passing through said solenoids,

means for varyingthe tension in said rod,

a sound reproducing diaphragm and a connection between a point in said armature and said sound reproducing diaphragm for reproducing the sound vibrations existent in said armature.

2. An electromagnetic sound reproducing device comprising in combination a permanent ring shaped magnet pole pieces connected with said magnet in diametrically opposed positions, a pair of solenoids se- 

